Lambert-Eaton Myasthenic Syndrome, Botulism, and Immune Checkpoint Inhibitor-Related Myasthenia Gravis.

PURPOSE OF REVIEW

This article reviews the pathophysiology, epidemiology, clinical presentation, diagnosis, and treatment of Lambert-Eaton myasthenic syndrome (LEMS) and of botulism, and immune-related myasthenia gravis (MG) occurring in the context of immune checkpoint inhibitor therapy for cancer.

RECENT FINDINGS

The suspicion that LEMS is rare but also likely underdiagnosed is supported by recent epidemiologic data. A validated, LEMS-specific scale now exists to assess and monitor disease, and symptomatic and immunomodulatory treatments are available. As presynaptic disorders of neuromuscular transmission, LEMS and botulism share electrodiagnostic abnormalities but have important distinguishing features. Knowledge of the clinical features of botulism is needed, particularly with continued cases of infant botulism, the opioid epidemic increasing the incidence of wound botulism, and medical use of botulinum toxin, which may cause iatrogenic botulism. Foodborne botulism remains rare. Prompt recognition of botulism and administration of antitoxin can improve outcomes. MG may be exacerbated or may present de novo in the context of immune activation from immune checkpoint inhibitor therapies for cancer. Immune-related MG commonly overlaps with myositis and myocarditis. Corticosteroids typically result in improvement. However, immune-related MG can be more fulminant than its idiopathic counterpart and may cause permanent disability or death.

SUMMARY

The diagnosis of LEMS, botulism, or immune-related MG can generally be made from the patient's history, supplemented with directed questions, a physical examination designed to demonstrate abnormalities, and laboratory and electrodiagnostic testing. Early diagnosis and carefully selected treatment not only improve outcomes of the neuromuscular disease but can affect the prognosis of underlying malignancy, when present.